What is Blog?

Alright, so the discussion from the previous post has made me suspect that I don't necessarily know what makes a blog function: what are the necessary conceptual components?

-An opinion: Does a blog have to offer a particular or personal lens or perspective for interpreting information?

-A subject: Does a blog have to be about something?

-Comments: Is a blog without comments just a regularly updated website?

-Context: Does a blog need links to other blogs in order to define the cultural space that it occupies (and is this just another way of saying that a blog must contain an imbedded perspective/implicit opinion)?

Back to the chair and pipe...